For the uplink of future broadband systems, single-carrier based approaches with orthogonal frequency division are of interest. These approaches, particularly Interleaved Frequency Division Multiple Access (IFDMA) and its frequency-domain related variant known as DFT-Spread-OFDM (DFT-SOFDM), are attractive because of their low peak-to-average power ratio (PAPR), frequency domain orthogonality between users, and low-complexity frequency domain equalization. Collectively, single carrier based approaches with orthogonal frequency division may be known as single carrier based frequency division multiple access (SC-FDMA).
A DFT-SOFDM modulation scheme has been proposed for uplink transmissions over an air interface in the 3GPP (Third Generation Partnership Project) E-UTRA (Evolved UMTS Terrestrial Radio Access) communication system. In a DFT-SOFDM communication system, a frequency bandwidth is split into multiple contiguous frequency sub-bands, or sub-carriers, that are transmitted simultaneously. These sub-carriers are orthogonal to each other. A user may then be assigned one or more of the frequency sub-bands for an exchange of user information, thereby permitting multiple users to transmit simultaneously on the different sub-carriers. Additional sub-carriers are reserved for transmission of control data.
In DFT-SOFDM, uplink control data may be divided into two categories. A first category, data-associated control data, is control signaling (i.e., control data) that is always transmitted with, and used in the processing, of an uplink user data packet. Examples of this control data include transport format, new data indicator, and MIMO parameters. It has been proposed that all uplink transmission parameters be controlled by a Node B since it may be costly to provide reliable control data.
A second category of control data, that is, control data not associated with user non-control data, also known as user data non-associated control data, is control data that is transmitted independently of an uplink user data packet. Examples of this control data include acknowledgments (ACK/NACK), Channel Quality Information (CQI), and Multiple-Input Multiple-Output (MIMO) codeword feedback. In the absence of an uplink non-control data transmission, this control data is transmitted in a frequency region reserved for control data. Specifically, it has been proposed to utilize resources on the top and bottom of the frequency band for such control transmissions, with half of the transmission in a top resource block (RB) (e.g., 12 contiguous subcarriers) of the band during a first 0.5 ms slot and the second part of the transmission in a bottom RB of the band in the second 0.5 ms slot of the subframe. This achieves both frequency diversity and preserves single carrier transmission.
A problem exists for non-data-associated control data in that for small total bandwidths (e.g., 6 resource blocks (RBs)) the overhead for 1 RB top and 1 RB bottom is excessive. A second problem is that for odd number of RBs assigned for control, the top and bottom each will have e.g., 0.5, 1.5, 2.5, . . . RBs. Non-integer RBs (e.g., 6 subcarrier) on each of top and bottom may make CDM multiplexing of control between users more difficult. Particularly, it may be desired to CDM multiplex a number (e.g., 6-8) of users within each RB, and fewer than the desired number of users may be multiplexed in 0.5 RB (e.g., 6 subcarriers).
Therefore a need exists for a method and apparatus for non-data-associated control data within a frequency division multiple access communication system that alleviates the above mentioned problems.